EP0042760B2 - Continuous process for the manufacture of cyanuric acid - Google Patents

Continuous process for the manufacture of cyanuric acid Download PDF

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Publication number
EP0042760B2
EP0042760B2 EP81302821A EP81302821A EP0042760B2 EP 0042760 B2 EP0042760 B2 EP 0042760B2 EP 81302821 A EP81302821 A EP 81302821A EP 81302821 A EP81302821 A EP 81302821A EP 0042760 B2 EP0042760 B2 EP 0042760B2
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EP
European Patent Office
Prior art keywords
reaction mixture
cyanuric acid
circulating
urea
heat exchanger
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EP81302821A
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German (de)
English (en)
French (fr)
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EP0042760B1 (en
EP0042760A1 (en
Inventor
Elizabeth Alice Bagnall
Basil Anthony Guiliano
Henry Albert Pfeffer
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Olin Corp
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FMC Corp
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
    • C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
    • C07D251/12—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
    • C07D251/26—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
    • C07D251/30—Only oxygen atoms
    • C07D251/32—Cyanuric acid; Isocyanuric acid

Definitions

  • This invention relates to a continuous process for the manufacture of cyanuric acid from urea and/or biuret by the pyrolysis of a solution of urea and/or biuret dissolved in an inert solvent.
  • cyanuric acid can be produced by the pyrolysis of urea. This reaction may be expressed by the equation:
  • the resulting product, cyanuric acid which has the empirical formula, C 3 H 3 0 3 N 3 , Is generally represented structurally either as: or
  • the pyrolysis can be carried out either in a dry state, that is, in the absence of a solvent, such as is described in U.S. Patent No. 2 943 088, issued to R. H. Westfall on June 28, 1960, or in the presence of various organic solvents, such as described in U.S. Patent No. 3 065 233, issued to Hopkins et al. on November 20, 1962; U.S. Patent No. 3 117 968, issued to Merkel et al. on January 14, 1964; U.S. Patent No. 3 164 591, issued to Walles et al. on January 5, 1976; or British Patent 950, 826, issued to Whiffen & Sons, Limited on February 26, 1964.
  • cyanuric acid A large range of products, in addition to cyanuric acid, is produced. These products may include the amino substituted cyanuric acids, commonly referred to as amides of cyanuric acid, namely ammelide, ammeline and melamine, as well as other undesirable by-products, such as ammonium carbamate, melam and other condensation products.
  • amides of cyanuric acid namely ammelide, ammeline and melamine
  • cyanuric acid In order to obtain a purified cyanuric acid, it is the custom in the art to treat crude cyanuric acid to an acid digestion.
  • the crude cyanuric acid is digested in a strong acid bath, for example, 3 - 15 % sulfuric or hydrochloric acid.
  • This acid treatment selectively hydrolyzes the acid-soluble, cyanuric acid amides, that is, ammelide and ammetine, and converts them to cyanuric acid.
  • an acid digestion step is required where the concentration of ammelide or ammeline exceeds 1 % by weight of the cyanuric acid product.
  • cyanuric acid may be manufactured of such purity and freedom from cyanuric acid amides that acid digestion of the cyanuric acid product is not required if urea is heated in an inert solvent therefor at temperatures of 200°C - 250°C. under subatmospheric pressures.
  • Sulfolane is suggested as a suitable solvent.
  • the cyanuric acid crystallizes from the reaction mixture in a crystal separation zone as a mash and is transferred to a falling film evaporator.
  • the mash, containing crystallized cyanuric acid is freed from solvent in the falling film evaporator and the solvent is returned to the reaction zone after condensation.
  • One disadvantage of this process is that pluggage of the reactor tubes may occur, which could lead to the formation of hot spots, short circuiting and reduction in the rate of ammonia remowal. In this process, the ammonia may be entrained in the reaction mixture for a substantial time before escaping to the gas space.
  • a continuous process for the selected conversion of urea and/or biuret into cyanuric acid containing less than about 1 % aminotriazines comprises:
  • the solvent used is an alkyl sulfone having the formula:
  • each of R 1 and R 2 is lower alkyl or R 1 and R 2 together form a cyclic lower alkyl sulfone in which the sulfur atom is part of the ring.
  • the heat exchanger in step (a) is preferably at substantially atmospheric pressure and the forced circulation evaporative crystallizer body at subatmospheric pressure, whereby ammonia gas is removed from the reaction mixture as it enters the crystallizer body and is withdrawn from the system.
  • the heated reaction mixture from the heat exchanger enters the evaporative crystallizer body as a liquid stream below and preferably close to the surface level of the reservoir in the bottom section of the crystallizer.
  • the liquid stream of reaction mixture is directed into the crystallizer in a manner to maximize agitation of the reaction mixture.
  • the separation in (g) may be achieved by pumping the slurry to a filter or centrifuge to separate the cyanuric acid product from the residual reaction mixture.
  • the present invention enables the acid digestion step to be eliminated, because of the purity of the cyanuric acid produced. Moreover, the ammonia formed upon pyrolysis of the reaction mixture can be rapidly removed, thereby reducing the formation of undesirable cyanuric acid amides.
  • urea and/or biuret are dissolved in the sulfone solvent, which is capable of dissolving urea or biuret in substantial quantities, and in which the final product, cyanuric acid, is relatively insoluble, and which has a boiling point such that it does not boil at atmospheric pressure at the operating temperature of the process, that is, 180°C - 250°C.
  • Suitable sulfones include dimethyl sulfone, dipropyl sulfone and tetramethylene sulfone (sulfolane), the latter being especially preferred.
  • the solution of urea and biuret is made up in the desired solvent in a feed tank 4 that is external of the circulating loop formed by circulating pump 10, conduits 13, 14 and 15 between the heat exchanger 6 and crystallizer body 5.
  • the temperature of the heat exchanger 6 is maintained by the heat source 8.
  • the reaction mixture is metered from the feed tank to the circulating reaction mixture at a rate which permits one to maintain the surface level of the liquid reservoir in the evaporative crystallizer body as desired.
  • the cyanuric acid will precipitate from the reaction mixture as it circulates to form a slurry, and the concentration of cyanuric acid in the circulating slurry may be varied by adjusting the concentration of urea and/or biuret in the feed solution. It has been found that concentrations between about 5 and about 40 weight percent urea in the solvent gives good results with concentrations of 30 - 35 weight percent being particularly preferred.
  • the reaction mixture can be circulated rapidly by the pump 10 at a linear velocity of about 1.2 to 3 meters per second to maintain the cyanuric acid in suspension and provide sufficient agitation to assure that the temperature within the circulating reaction mixture is kept as uniform as possible.
  • Circulation rates under 1.2 meters per second should be avoided as the cyanuric acid crystals will settle from suspension.
  • Particularly preferred are circulation rates within the range of about 1.5 meters per second to about 3 meters per second. At these velocities, the entire volume of the reaction mixture is circulated from about once to about three times each minute.
  • the ammonia that is liberated during pyrolysis is removed from the reaction mixture as it enters the crystallizer which is maintained at a reduced pressure, preferably in the range of 20 to 53.3 kPa (150 - 400 mm Hg).
  • the liquid stream of the reaction mixture containing crystallized cyanuric acid in suspension enters the crystallizer body at a point that is below the surface level of the reservoir of reaction mixture 16.
  • the liquid stream will enter tangent to the cylindrical wall of the crystallizer body as shown in Figures 2 and 3 so as to form a turbulent vortex of slurry having sufficient surface area to permit the rapid disengagement of ammonia from the reaction mixture.
  • the high velocity flow around the loop between the heat exchanger 8 and the crystallizer body maintains the cyanuric acid in suspension and ensures that any ammonia which may be entrained in the reaction mixture will be subject to a reduced absolute pressure of 20 to 53.3 kPa (150 - 400 mm Hg) every minute.
  • inert solvent is vaporized as the reaction mixture enters the crystallizer. This volatilized solvent passes with the disengaged ammonia overhead to a condenser 7 where the solvent is condensed and returned to the crystallizer. The ammonia is vented from the condenser 7.
  • Both the circulating loop between the heat exchanger and crystallizer body, as well as the crystallizer body itself, are insulated. This combined with the rapid circulation of the reaction mixture through the heat exchanger reduces temperature fluctuation throughout the reaction mixture so that the pyrolysis reaction proceeds at a constant temperature ( ⁇ 2°C) and uniform rate.
  • the reaction temperature is maintained within the range of about 180°C to about 250°C the total residence time of the reaction mixture is between one and four and preferably between one and three hours based on the volumetric feed rate. It is preferred for optimum performance of the process that the reaction temperature be within the range of about 200°C to about 220°C, and that the absolute pressure within the crystallizer body be maintained between about 26.7 and 33.3 kPa (200 - 250 mm Hg).
  • the circulating slurry of cyanuric acid is continuously removed at a constant rate and is transferred by the pump 11 to a separation zone 9 where the crystalline cyanuric acid is separated (by filtration or centrifugation) from the liquid reaction mixture.
  • the cyanuric acid product may be dried and the separated liquid reaction mixture containing 1 % to 8 % unreacted urea and/or biuret is returned to the feed tank 4.
  • Urea and additional solvents, as required, are continuously added to the feed tank.
  • the reaction mixture from the feed tank 4 is added to the circulating slurry of cyanuric acid at the same rate that the cyanuric acid slurry is removed to the separator zone.
  • the solution of urea enters the crystallizer body at a tangent to the cylindrical wall and beneath the surface of the liquid in the crystallizer, as is shown in Figures 2 and 3.
  • the temperature of the circulating reaction mixture is maintained at 205°C by the heat input as it passes through the heat exchanger and the absolute pressure within the crystallizer body is 23.3 kPa (175 mm Hg).
  • the cyanuric acid slurry withdrawn is pumped to a centrifuge 9 and the cyanuric acid separated by the centrifuge dried in the vacuum oven to give a product analyzing 0.55 % aminotriazine.
  • the yield based upon urea conversion is 86 %.
  • the liquid reaction mixture from the centrifuge is returned to the feed tank 4.
  • Urea and sulfolane are added to the feed tank as required to maintain the concentration of urea and/or biuret in the solvent at 20 weight percent.
  • biuret may be continuously pryolyzed to form cyanuric acid.
  • Example 1 A laboratory scale version of the process described in Example 1 is performed with the temperature being held at 195°C and the absolute pressure above the liquid surface at 13.3 kPa (100 mm Hg). The concentration of urea in the feed is 30 weight percent. Cyanuric acid yields of 89 % were obtained with a two hour residence time. In a similar manner, good yields of cyanuric acid may be obtained at 180°C and 20 kPa (150 mm Hg) by increasing the residence time to three hours.
  • Example 1 The process described in Example 1 above may be repeated except that the temperature of the circulating reaction mixture is maintained at 220°C, and the absolute pressure within the evaporative crystallizer body is maintained at 33.3 kPa (250 mm Hg). Cyanuric acid may be isolated in good yield as a white crystalline solid of large particle size (94 % retained on a 200 U.S. mesh screen, that is, 74 micrometers).

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
EP81302821A 1980-06-25 1981-06-23 Continuous process for the manufacture of cyanuric acid Expired EP0042760B2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US162718 1980-06-25
US06/162,718 US4294962A (en) 1980-06-25 1980-06-25 Continuous process for the manufacture of cyanuric acid

Publications (3)

Publication Number Publication Date
EP0042760A1 EP0042760A1 (en) 1981-12-30
EP0042760B1 EP0042760B1 (en) 1984-10-10
EP0042760B2 true EP0042760B2 (en) 1990-02-28

Family

ID=22586861

Family Applications (1)

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EP81302821A Expired EP0042760B2 (en) 1980-06-25 1981-06-23 Continuous process for the manufacture of cyanuric acid

Country Status (7)

Country Link
US (1) US4294962A (ja)
EP (1) EP0042760B2 (ja)
JP (1) JPS596307B2 (ja)
CA (1) CA1141762A (ja)
DE (1) DE3166580D1 (ja)
ES (1) ES503357A0 (ja)
MX (1) MX158761A (ja)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6115401A (ja) * 1984-06-30 1986-01-23 Murata Mfg Co Ltd 分布定数形フイルタ
US4567258A (en) * 1985-04-18 1986-01-28 Olin Corporation Process and apparatus for producing cyanuric acid
CN118812397A (zh) * 2024-07-30 2024-10-22 黔南民族师范学院 一种草酸脲合成方法

Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3065233A (en) * 1962-11-20
US3164591A (en) * 1965-01-05 Preparation of cyanuric acid
US3154545A (en) * 1964-10-27 Process for preparing cyanuric acid
US3236845A (en) * 1963-04-26 1966-02-22 Grace W R & Co Production of cyanuric acid from urea
US3297697A (en) * 1963-06-20 1967-01-10 Nipak Cyanuric acid production
DE1770827C3 (de) * 1968-07-09 1975-02-06 Basf Ag, 6700 Ludwigshafen Verfahren zur Herstellung von Cyanursäure
US3563987A (en) * 1969-04-01 1971-02-16 Fmc Corp Preparation of cyanuric acid
DE2300037A1 (de) * 1973-01-02 1974-07-04 Basf Ag Verfahren zur kontinuierlichen herstellung von cyanursaeure
NL7405629A (nl) * 1974-04-26 1975-10-28 Stamicarbon Werkwijze voor het bereiden van cyanuurzuur.
US4237285A (en) * 1979-06-06 1980-12-02 Olin Corporation Process for the production of concentrated cyanuric acid slurries
US4303494A (en) * 1979-08-06 1981-12-01 Mobil Oil Corporation Continuous reaction/separation method for nucleated growth reactions

Also Published As

Publication number Publication date
ES8205400A1 (es) 1982-06-01
EP0042760B1 (en) 1984-10-10
US4294962A (en) 1981-10-13
ES503357A0 (es) 1982-06-01
JPS5756471A (en) 1982-04-05
MX158761A (es) 1989-03-13
DE3166580D1 (en) 1984-11-15
EP0042760A1 (en) 1981-12-30
JPS596307B2 (ja) 1984-02-10
CA1141762A (en) 1983-02-22

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